NITROGEN; THE COMPOSITION OF AIR 



23 



cise 14), and invert the jar in a pan containing water to the 

 depth of an inch or two. Then raise the temperature of the 

 water in the pan to boiling, and continue the boiling for 15 or 

 20 minutes. What collects in the upper part of the inverted 

 glass jar? 



Let the jar and its contents become moderately cool; then 

 cover the mouth of the jar with moist paper, and remove the 

 jar to a pail of water. Now transfer the gas, under water, from 

 the jar to a test tube of water (see Fig. 78, 102, of the text). 

 Close the test tube with the thumb, invert it, and put into the 

 gas a burning splinter. Does the gas act like air, or not? 



EXERCISE 19 



NITROGEN; THE COMPOSITION OF AIR 



Apparatus and Materials. Test tube, beaker, 10% solution of 

 potassium hydroxide (or sodium hydroxide), "mossy" (granulated) 

 tin (or iron filings), pail of water, graduated cylinder. 



a. We can find out what the nitrogen of the air is like by 

 removing the oxygen. Certain metals moistened with a solu- 

 tion of potassium hydroxide or sodium hydroxide 



readily unite with the oxygen. We make use of 

 this fact in the following experiment (Fig. 13) : 



Into a test tube put a piece of "mossy" tin of 

 such a size that it sticks slightly when pushed 

 into the tube. Pour into the test tube about 

 10 cu. cm. of 10% potassium hydroxide solu- 

 tion, wetting the tin thoroughly; then pour the 

 solution out into a small beaker. Now set the 

 tube, mouth down and vertical, into the beaker, 

 and let it stand over night. 



b. Wliat change do you notice? By holding 



your ruler upright beside the test tube estimate FIG. is. 



